This invention relates to a method and apparatus for measuring the clearance between the spindle of a turbine and the stationary parts therein. More particularly, the method and apparatus will determine the required distance between the centerline of the spindle and the stationary parts to prevent damaging rubbing from occuring during operation.
The turbines used to generate electricity are comprised of a high pressure component and a low pressure component. The high pressure component consists of a super pressure turbine and a high pressure turbine which have a common spindle that extends beyond the high pressure turbine into the generator component located at that end. The total spindle is made up of three separate shaft sections, one for each turbine and one for the generator, which form a continuous shaft with bearings located at each end of each section.
In the super pressure turbine, the various turbine blades rotate within circumferential grooves in the inner cylinder, which inner cylinder carries fixed blades with stationary sealing elements provided therebetween to seal steam leakage. The stationary sealing elements, or packing gland seals, are fixed inside seal holders in the inner cylinder, and fit next to, and have very close clearances with, packing segments on the spindle. Clearances between the sealing elements and the packing segments must be in the order of 0.030 inches to prevent damage through contact between the two. When the inner and outer cylinders are assembled around the spindle, these clearances must be precisely controlled to prevent the stationary sealing elements from wiping against and damaging the packing segments. This is also the case for the clearance required at the inner gland seals at each end of the turbine, and any wiping of the sealing grooves on the spindle by the fixed inner gland seals will result in damage to the spindle. Minor wipes cause leakage which reduces efficiency, while major wipes will cause extesive damage to the spindle.
Whenever a super pressure turbine is scheduled for an overhaul, many problems can surface. If, for example, inspection of the existing seals shows an unusual wear pattern on certain seals, this would indicate that there is misalignment between the rotating spindle and the stationary parts. Correction of this problem requires major realignment of the stationary parts with respect to each other and to the spindle. In this case, major realignment refers to both a stationary parts alignment, i.e. the outer cylinder with gland packing carriers and the inner cylinder with stationary blade rings and a balance piston seal carrier, with respect to each other, and a coupling alignment. During the stationary parts alignment, the position of each of these parts must be measured with respect to the centerline of the spindle. These measurements are taken with the top halves of the turbine on and bolted tight (called tops-on readings) in order to eliminate cylinder sag and out of roundness. The measurement procedure normally also requires a set of readings be taken with tops-off for comparison purposes.
Heretofore, the measurements required to perform a major alignment were obtained by either optical methods or direct measurement. In either case, both tops-on and tops-off readings are taken. The optical methods included use of either the Farand scope, which is similar to a transit, or, when the turbine is large enough, a laser beam and targets mounted in the bore of each stationary part with readings being taken by line of sight. The direct measurement method is also only used when the turbine is large enough and accomplished by means of a tight wire (a 16 gauge piano wire tensioned by a 30 pound weight) placed on the turbine center and with a machinist or other individual crawling inside the turbine and taking readings to measure the distance from the wire to the bore of each stationary part with a micrometer.
In certain instances, when for example a Farand scope is not available or the turbine is too small, as with the super pressure turbine, boiler feed pump drive turbine or reactor feed pump drive turbine, for a machinist to crawl around inside with the tight wire or to allow positioning of the targets for the laser scope, none of the known methods are adequate and a new method and apparatus must be devised to allow the alignment readings to be obtained.